In a tape drive, such as a linear tape drive, the tape speed during operation is typically around 2-10 meters per second, with the reels rotating at around 10-70 times per second. Additionally, on a typical half inch tape, there may be 1000 or more data tracks spaced laterally across the tape. Because of these speeds, lateral tape position errors are likely to occur. And because of the density of data tracks, the lateral tape position errors are likely to cause track misregistration.
One type of error is caused by vibration events that are not directly related to the tape drive operation or tape speed. In general, in the low frequency region below 500 Hz, these vibration events could be generated by external vibration to the tape drive, or electric cooling fan vibrations. In the high frequency region greater than 500 Hz, these vibration events could be the resonance of the tape in the lateral direction, or the resonance of the tape guides.
However, there is also a second type of event that can occur with respect to the operation of the tape drive. In many cases, these events are related to the actual operation of the tape drive at higher speeds and can introduce vibration errors or transient tape motions. In general, in the low frequency region below 500 Hz, these events could be generated from rotating frequency of tape guides, or rotating frequency of tape reels. In the high frequency region greater than 500 Hz, these events could be generated by roller bearing defects, reel motor cogging, tape edge wear, reel flanges scraping tape edge, roller surface contamination and stiction to tape surface, or other irregular geometry causing fast transient tape motions. For example, in a single reel tape cartridge drive, the tape drive may utilize grabbers or bucklers to thread the tape from the cartridge to the drive reel. As such, there is an unavoidable grabber or buckler mismatch to the drive reel hub. This sudden protrusion or recession on the reel hubs can cause sudden disturbance to the tape motion longitudinally and/or laterally. The lateral tape motion can be so fast that the head of the tape drive cannot accurately follow and read from or write to the tightly spaced adjacent data tracks.
Presently, tape drives utilize a controller to move an actuator and the read/write head to follow the tape position errors. In this manner the low frequency tape position errors can be successfully eliminated. For example, markings known as Position Error Signals (PES) are provided at fixed intervals along the tape and a controller can sample the PES and output a control demand to the actuator based on a constant sample rate. This results in a set of coefficients that are fixed for a given controller design. However, due to the variation of tape speed in a tape drive, the PES frame rate and controller sample rate may become asynchronous to each other thereby resulting in additional undesirable delays for the controller. In other words, the controller may be reacting to an error scenario, such as a tape location shift, that has changed during the asynchronous delay. Thus, a controller's suppression function may be either too small or too large with respect to the real-time position of the tape.